The present invention relates to a railway information transmission method and system for readily sensing trouble on a transmission path in a railway information transmission system wherein information is transmitted between equipment on the ground and equipment on a train by a consecutive transmission mode.
The transmission modes used in a railway system between on-vehicle control equipment on a train and control equipment on the ground include a consecutive transmission mode and a point transmission mode. With the consecutive transmission mode, the same information is repeatedly transmitted to the train at predetermined time intervals, thereby to ensure the reliability of the information transmission for the reason, for example, that trouble with the equipment can be detected easily from the interruption of transmission of the transmission information.
An example of train control based on the consecutive transmission mode, such as is used at present, is represented by the conventional automatic train control system (ATC system). In this type of system, a control method for establishing the speed limit of each section along a track is based on an analog information transmission wherein speed limit information is transferred to the train by transmitting and receiving a signal having a frequency corresponding to the speed limit at the particular section along the track.
In contrast, the official gazette of Japanese Patent Application Laid-open No. 128760/1991 discloses, by way of example, a digital information transmission method wherein information is transferred in such a way that a signal wave obtained by modulating speed limit information etc. as digital information is transmitted from ground control equipment, and the transmitted signal wave is received and demodulated by the on-vehicle control equipment of the train.
In general, in transmitting digital information, a method of detecting an error in the information, in the case where the content of the information has been destroyed or changed by a bit error, is performed wherein equipment on the transmission side transmits the information while affixing thereto a redundant code for error detection, such as a CRC (cyclic redundancy check) code, and the equipment which receives the transmitted information checks the contents of the error detecting code and the information so as to avoid using any erroneous information for processing.
Regarding a method for affixing such a redundant code to transmitted information, the official gazette of Japanese Patent Application Laid-open No. 1364725/1988, for example, discloses a redundant code processing method wherein transmission equipment forms a matrix by the use of information to-be-communicated and creates redundant codes in the row and column directions of the matrix, and then it transmits the resulting information; and, reception equipment similarly forms a matrix and creates redundant codes in the row and column directions of the matrix for the received information, and it correlates the created redundant codes with the received ones, so as to detect and correct an error in the received information.
In train control, for example, in a system where safety control is important, such as an automatic train control system (ATC system), it is required that the ground equipment should stop the output of information to the train in case of trouble in the transmission thereof, and it should allow the train to judge whether the trouble is in the ground equipment or whether the occurrence of the trouble is in the train, lest the train be operated with poor safety on account of repeated transmissions of the same information attributed to trouble in the ground equipment. In order to satisfy such a requirement, the ground equipment uses devices of higher reliability relative to the whole system. For this reason, the ground equipment becomes complicated in construction and is expensive.
As one method of curtailing the cost of a railway system, it is considered desirable to endow the ground equipment with a simple processing architecture.
However, in a case where the processing, in which the information is repeatedly sent while being updated, as in the consecutive transmission mode, is executed by the use of such equipment, trouble might occur to bring about a state where information which has been transmitted previously is subjected to transmission processing in a current transmission procedure as if it were new information. On such an occasion, since error detection means for the CRC code or the like is an expedient used only for detecting a bit error in the information to-be communicated, no checking method based solely on the CRC code or the like can detect trouble in the equipment, except when information transmitted previously undergoes a bit error.
An object of the present invention is to realize a simple way of detecting trouble in the transmission path, and, further, to enhance the safety of train service based on automatic train control or the like, in a railway information transmission method and system wherein information is transmitted between control equipment on a train and control equipment on the ground by the consecutive transmission mode.